The present invention relates to sewage treatment apparatus and methods and more particularly to lysing mills and systems for lysing biological sludges, biological floc and mixed liquor, and dewatering sludge. The present invention also relates to apparatus and methods for rupturing microbial cells (lysis) and separating the cellular membrane from the cytoplasm in the production of cell-free extracts, serum and nutriments from fermentations, cell cultures and tissue. Further, the present invention relates to apparatus and methods for disintegrating solid particles in the production of liposomes and submicron dispersions.
In recent years, the demand for more effective and efficient sewage treatment facilities has grown. One of the most important aspects of sewage treatment is the removal and disposal of biosolids. It has long been recognized that biological respiration and synthesis occurring in the aeration system of a secondary biological wastewater treatment plant converts the organic material it receives in the sewerage it treats to carbon dioxide. water and new cells. The amount of biodegradable organic material in the sewerage treated can be indirectly determined as biological oxygen demand (BOD). Much of this BOD (40 to 60%) is transformed into new cells as a result of the aerobic respiration occurring in the treatment plant""s aeration system. These new cells (biosolids), which are produced daily, must be removed for the proper operation of the treatment plant. This waste stream is known as waste activated sludge. Merely separating and removing the biosolids translates to a substantial solid waste disposal problem, with a large portion of the mass of the biosolids being attributable to intracellular water. Accordingly, if the cell solids could be isolated and removed from the biomass leaving cellular water content to be returned to the processed wastewater, such separation would constitute a large reduction in the mass and volume of biosolids requiring disposal, e.g., in a landfill.
In the past, rotor and stator colloidal dispersion mills have been used for mechanically disintegrating suspended solid and liquid components of, e.g., wastewater sludge, paint, ink and the like to produce liquid suspensions with finely divided components. In U.S. Pat. No. 5,240,599, liquid containing immiscible liquid(s) and/or partially dispersed solid particulate component(s), are propelled by a rotor against the interior surface of a concentric stator ring having a plurality of radial passageways or slots intermittently spaced around its circumference. The slots have a constant, relatively narrow width compared to the circumference of the stator. The rotor is typically propelled at a very high velocity, e.g., usually between 5,000 to 12,000 feet per minute. As a result, the fluid and entrained immiscibles to be processed are subjected to strong centrifugal forces which induce an outward flow through the narrow slots of the stator. When the rotor and stator slots come into alignment, the fluid is ejected from the rotor slots into the stator slots. All components carried in the ejected fluid have an initial resultant velocity attributable to the radial and tangential velocity imparted by the rotor. Predominantly tangential motion causes some portion of the immiscibles carried in the flow through the rotor slot to impinge on the interior radial surface of the stator slot emanating from the trailing edge of the slot, fracturing them into smaller sub-parts. This action is applicable to particles or to globules of undissolved fluids which can be broken down by impinging them against the stator slot walls.
Workers in the field of cell disruption have shown that pressures on the order of 5,000 to 20,000 psia are necessary to rupture bacterial cell membranes. Traditional lysing processes rely on brute-force techniques to generate high-pressures. For example, hydraulic cylinders raise the pressure of a flow stream up to the required pressure of 5,000 to 20,000 psia. The liquid is then forced through an orifice, split into two streams which are brought back together, and made to impinge against one another. This technique is far more energy intensive then comparable lysing with a dispersion mill, which produces these high pressures for a brief instant with each impact.
U.S. Pat. No. 5,522,553 sought to improve the lysing capacity of a dispersion mill of the type with a slotted rotor and stator by changing the design of the slots in the stator. The ""553 patent describes chamfers on the leading edges of the stator slots to permit fluid flow from the rotor into the stator which is of longer duration, of greater volume, and along a path resulting in a impact angle of 90xc2x0. The impact angle of 90xc2x0 of U.S. Pat. No. 5,522,533 generates greater stagnation forces that result in cavitation when the fluid accelerates away from the impact zone. Subsequent discharges into the stator slot increase ambient pressure around vapor cavities created by prior fluid injections into the slot and accelerate cavity collapse. This generates higher pressures through accelerated collapse and also through reentrant jet effects. The tremendous pressures associated with cavitation and reentrant jet effects result in shock waves which are transmitted through the fluid and lead to a disintegration of entrained particulates, such as cells. While the prior art referred to above is highly effective in cell lysing, improvements are always desirable to increase the efficiency and effectiveness of cell lysing apparatus, which is an objective of the present invention.
It is a further object of the present invention to incorporate a cell lysing apparatus into a wastewater processing train to produce a more efficient wastewater processing system. Another objective of the invention""s cellular disruption is the elimination of the occurrence of bulking arising from the production of excess filamentous organisms in an aerobic wastewater treatment system.
It is another objective of this invention to provide an efficient apparatus for microbial lysis and particle disintegration which is sufficiently small so as to be easily installed into existing wastewater treatment facilities with little or no modification of such facilities being required.
The present invention provides a novel means of operating an activated sludge wastewater treatment facility without the need to remove excess biological sludge. The present invention, through the induction of robust cavitation and impingement, ruptures the cells and fragments the particles in the waste activated sludge stream and recycles this processed/lysed material as food to the microorganisms that reside in the aeration system of the wastewater treatment plant. The recycling of the disintegrated waste activated sludge is not sufficient alone to eliminate the production of excess biosolids due to the composite metabolism of all the microorganisms residing in the wastewater treatment system. Therefore it is also part of the claimed invention that the continuous operation of the embodied apparatus generates conditions, where only specific species of microorganisms can exist and thrive. This method of operation artificially creates an endogenous phase of respiration, where the growth of cells does not cease, but where the rate, by which, microorganisms reproduce (biological respiration) is exceeded by the combination of natural cellular degradation and the rate of cellular disruption and lysis generated by the present invention. The invention""s capacity to produce cellular disruption also eliminates bulking, which arises from the production of excess filamentous organisms in an aerobic wastewater treatment system. The present invention, while providing an efficient and effective means of microbial lysis and particle disintegration, is physically modest in size and suitable for installation into existing wastewater treatment facilities without substantial modification thereof.